Implantable medical devices (“IMDs”) configured to be implanted in a human body and to perform one or more therapeutic functions, such as drug delivery, cardiac pacing, cardiac defibrillation, neural stimulation, and the like, are known. Additionally, IMDs are known that can be implanted within a patient's body for measuring one or more physiologic parameters. For example, sensors or transducers can be implanted in the body for monitoring a variety of properties, such as temperature, blood pressure, strain, fluid flow, chemical properties, electrical properties, magnetic properties, and the like. Such IMDs can be placed at various locations throughout a person's body, thereby providing a heterogeneous mix of physiologic data. The IMDs making up such systems typically include components adapted for bi-directional wireless communication, allowing the IMDs to transmit data to and receive data from other IMDs and/or devices external to the patient.
The foregoing types of IMDs used for sensing physiological parameters are typically size and space constrained, which in turn, constrains the size and capacity of the power supply (e.g., battery) for providing power to the various IMD components and circuitry. Accordingly, such IMDs must be maintained in a low power or powered off state for the majority of the time, and are ideally energized only to perform their designated functions, after which time they must be returned to their powered down state.
Thus, a need exists for systems and methods for activating IMDs from a low power or powered off state that require minimal power and physical space within the IMD housing.